sudo fdisk -l

Disk /dev/sda: 750.2 GB, 750156374016 bytes
255 heads, 63 sectors/track, 91201 cylinders, total 1465149168 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disk identifier: 0x7d468a6b

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *        2048      206847      102400    7  HPFS/NTFS/exFAT
/dev/sda2          206848   614402047   307097600    7  HPFS/NTFS/exFAT
/dev/sda3       614402048   921602047   153600000    7  HPFS/NTFS/exFAT
/dev/sda4       921604094  1465147391   271771649    5  Extended
Partition 4 does not start on physical sector boundary.
/dev/sda5       921604096   952852479    15624192   82  Linux swap / Solaris
/dev/sda6       952854528  1465147391   256146432   83  Linux

Disk /dev/sdb: 15.5 GB, 15518924800 bytes
64 heads, 32 sectors/track, 14800 cylinders, total 30310400 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x2052474d

This doesn't look like a partition table
Probably you selected the wrong device.

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1   ?     6579571  1924427647   958924038+  70  DiskSecure Multi-Boot
/dev/sdb2   ?  1953251627  3771827541   909287957+  43  Unknown
/dev/sdb3   ?   225735265   225735274           5   72  Unknown
/dev/sdb4      2642411520  2642463409       25945    0  Empty

Partition table entries are not in disk order